1. Field of the Invention
The invention relates to wireless communication devices. More particularly, the invention relates to receivers in multimode wireless communication devices.
2. Description of the Related Art
A vast array of wireless communication devices is available for consumer use. The communication devices include pagers, two-way radios, and wireless phones, such as cordless phones, cellular phones, and personal communications service (PCS) phones.
The multiple wireless devices typically operate in different frequency bands and different communication systems that operate according to detailed specifications. Within a particular type of wireless communication device there may be a number of different specifications that make it difficult for a single device to operate in more than one communication system. For example, in the field of wireless phones there are numerous specifications and standards.
Wireless phone systems may be based on code division multiple access (CDMA), time division multiple access (TDMA), orthogonal frequency division multiplexing (OFDM), frequency modulation (FM), or some other modulation techniques. A wireless phone configured to operate within a Global System for Mobile Communications (GSM) system may be inoperable in a CDMA system.
A GSM system is typically designed to support one or more GSM standards, such as the standards offered by the “3rd Generation Partnership Project (3GPP)” and embodied in the 3GPP specification where the term “3GPP specification” refers to all GSM specifications including those covering GSM Evolution (GSM EDGE), Global Packet Radio Service (GPRS), and GSM 3G. The 3GPP specification is provided in a set of documents provided by Technical Specification Groups (TSG) including specifications in series 01 through 13 for GSM only prior to Rel-4, series 21 through 35 for 3G/GSM R99 and later, and series 41 through 52 for GSM only for Rel-4 and later.
A CDMA system may be designed to support one or more CDMA standards such as (1) Telecommunications Industry Association (TIA)/Electronic Industries Association (EIA) “TIA/EIA-95-B Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System” (the IS-95 standard), (2) the standard offered by a consortium named “3rd Generation Partnership Project” (3GPP) and embodied in a set of documents including Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214 (the W-CDMA standard), (3) the standard offered by a consortium named “3rd Generation Partnership Project 2” (3GPP2) and embodied in a set of documents including “C.S0002-A Physical Layer Standard for cdma2000 Spread Spectrum Systems,” the “C.S0005-A Upper Layer (Layer 3) Signaling Standard for cdma2000 Spread Spectrum Systems,” and the “C.S0024 cdma2000 High Rate Packet Data Air Interface Specification” (the cdma2000 standard), and (4) other standards.
Currently wireless devices, such as a wireless phone, may operate in a first mode but be capable of operating in a plurality of operating modes. When signal quality for a communication link using the first mode may degrades to an unacceptable quality of service, the wireless device can attempt to hand off the communication link from a base station in a first cell to a base station in a second cell. However, the second base station may operate in a different operating mode than the first base station. Thus it may not be possible for the wireless device to remain in the first operating mode. In such a case, the wireless device may need to negotiate a hand off to a base station using a second operating mode. Unfortunately, the first and second operating modes may use communication channels in different frequency bands and may also use incompatible modulation techniques.
As an example, a wireless phone operating in a GSM mode may establish a communication link in a first frequency band with a GSM base station. The wireless phone may then move to the edge of the GSM base station coverage area such that the quality of service of the communication link is degraded. The wireless phone may attempt to hand off the communication link to another GSM base station, but there may not be any other GSM base station that can provide a communication link having an improved quality of service. However, there may be a UMTS base station operating in a WCDMA mode that is able to provide to the wireless phone a communication link having an improved quality of service. However, the UMTS base station may operate in a frequency band that is different from the frequency band used by the GSM base station. Additionally, the WCDMA operating mode requires significantly different signal processing than the GSM operating mode.
The UMTS specification includes provisions for implementing a hand off from a WCDMA operating mode to a GSM operating mode. For example, one manner of accomplishing an inter-mode hand off is by using a compressed mode of operation. In compressed mode the WCDMA information is compressed into a segment of time to allow the wireless phone to simultaneously receive both GSM and WCDMA communications in a time duplexed manner. However, operating in the compressed mode is highly complex. Information in the WCDMA uplink and downlink are compressed to allow time division duplex operation. Additionally, the GSM operating mode uses time division duplex operation. The timing issues that must be controlled in the compressed operating mode make it difficult to implement a wireless phone using compressed mode.
In a second example, the wireless phone may implement two distinct receivers. A first receiver may operate in the GSM operating mode and the second receiver may operate in the WCDMA operating mode. The GSM and WCDMA receivers operate independently to receive and demodulate the respective signals. However, this design occupies a large volume within the wireless phone and minimizing total volume of the wireless phone is desired. Additionally, the two receivers operate simultaneously for only brief periods of time when the phone is negotiating an inter-mode hand off. Thus, the two receiver implementation provides a receiver that is idle for the majority of time. The additional parts needed for the two receiver implementation also increase the total cost of manufacturing the wireless phone.
Thus, what is needed is a manner of configuring a wireless device, such as a wireless phone, to simultaneously operate in multiple modes. The wireless device should be able to simultaneously communicate over multiple communication links using multiple communication modes. A wireless phone using the configuration should be able to simultaneously operate in a GSM mode and a WCDMA mode without using compressed mode. Thus, the wireless phone should be able to negotiate an inter-mode hand off without operating in compressed mode.